MongoDB driver pagination - mongodb

Question

Currently I am able to return all my products from the collection.
I however want to be able to return products that come after a specific product ID (which would be the last one on the client side so they could load more)
Current way (return all)
query := bson.M{}
var product ReturnedProdcut
var products []ReturnedProduct
cur, err := mg.Db.Collection("products").Find(c.Request().Context(), query)
if err != nil {
fmt.Println(err)
}
for cur.Next(c.Request().Context()) {
err := cur.Decode(&product)
if err != nil {
fmt.Println(err)
}
products = append(products, product)
}
// return products list in JSON format
return c.JSON(http.StatusOK, products)
New Way Attempt(return based on page)
afterID := c.QueryParam("afterID")
if afterID == "" {
// get from start of collection based on latest date
}
// get 10 products after this ID, if no ID then get from start
query := bson.M{}
var product ReturnedProduct
var products []Returnedproduct
//.find(afterId).limit(10) - something like this?
cur, err := mg.Db.Collection("products").Find(c.Request().Context(), query)
if err != nil {
fmt.Println(err)
}
for cur.Next(c.Request().Context()) {
err := cur.Decode(&product)
if err != nil {
fmt.Println(err)
}
products = append(products, product)
}
// return products list in JSON format
return c.JSON(http.StatusOK, products)

Answer 1

The official MongoDB Go driver also has a *FindOptions optional parameter you could also explore.
pageOptions := options.Find()
pageOptions.SetSkip(int64(page)) //0-i
pageOptions.SetLimit(int64(limit)) // number of records to return
cur, err := userCollection.Find(c.Request().Context(), bson.D{{}}, pageOptions)
if err != nil {
// handle error
}
defer cur.Close(ctx)
var products []Returnedproduct
for cur.Next(c.Request().Context()) {
var product Returnedproduct
if err := cur.Decode(&product); err != nil {
// handle error
}
products = append(products, &product)
}
if err := cur.Err(); err != nil {
// handle error
}

Answer 2

You may construct a query where _id is greater than afterID, in which case you should also specify sorting by _id. For sorting and for setting a limit, you may use options.FindOptions.
You also should use Cursor.All() to decode all results and not one-by-one.
This is how it could look like:
query := bson.M{"_id": bson.M{"$gt": afterID}}
opts := options.Find().
SetSort(bson.M{"_id": 1}).
SetLimit(10)
ctx := c.Request().Context()
curs, err := mg.Db.Collection("products").Find(ctx, query, opts)
if err != nil {
// Handle error
}
var products []Returnedproduct
if err = curs.All(ctx, &products); err != nil {
// Handle error
}
return c.JSON(http.StatusOK, products)